1. Field of the Invention
This invention relates to an apparatus for carrying out, at a constant rate, carrier gas feeding of injectors for capillary or micropacked gas-chromatographic columns, more precisely injectors of the so-called on-column type, as for instance described by Grob & Grob (Journal of Chromatography 151, page 311 (1978)).
In particular, this invention relates to a feeding apparatus of the described type, having new and improved features, capable of allowing better and more perfect operative efficiency of the injector-column unit to which this apparatus sends the carrier gas.
2. Description of the Prior Art
As it is known, the above described "on-column" type injectors are used to inject samples into capillary gas-chromatographic columns and are provided with a sealing element which is opened during injection and subsequently closed at the end of injection and during the whole period in which the sample, together with the carrier, constantly flowing into the injector, are introduced into the gas-chromatographic column, which is housed, in turn, in an oven with temperature varying according to a preset program.
Under these conditions, a pressure regulator operating at constant pressure allows maintaining gas constant rate only when operative conditions, and particularly, conditions of temperature and pressure of the system which is fed with gas are constant. This situation occurs, however, only during the sample injection stage, while during the subsequent stage, when a determined program of temperature variation in the column is followed, there are consequently variations in hydraulic resistance of the columns (viscosity variations in the carrier gas). As a result of these variations, the carrier gas rate changes simultaneously with the temperature variation of the column when the type of pneumatic control used keeps the pressure upstream of the column constant. In order to achieve the best possible operative conditions in the column, for the highest precision and reproducibility of results of analyses performed at the column outlet, it is necessary that the carrier gas is fed into the injector in such a way that a constant rate is reached at the column outlet both during the sample injection stage and during the subsequent processing stage in the gas-chromatographic column. Due to the fact that the sealing piece is opened during injection, feeding with carrier gas is not possible during the injection stage, although this kind of feeding may be performed after the injection stage when the carrier gas is exclusively conveyed into the column.